Host specialization is traditionally viewed as the pathway to speciation in parasitic plants. However, geographical and environmental changes can also influence parasite speciation through population isolation and secondary contact.
In a recent publication (Baena-Díaz et al, 2018; Scientific Reports) we investigated the impact of past climatic fluctuations, niche divergence, and host shifts on the patterns of genetic differentiation in the Psittacanthus schiedeanus mistletoe complex (Loranthaceae). This species complex is composed of two main genetic clusters with different climatic niche: P. calyculatus in dry pine-oak forests and P. schiedeanus in cloud forests. Interestingly, we found evidence of a third genetic cluster, with high levels of admixture between P. calyculatus and P. schiedeanus, thriving in xeric and tropical dry forests and infecting a different set of hosts (mainly species of Anacardiaceae, the cashew family). Coincidently, these areas are predicted to be the place of overlap in the distribution of P. calyculatus and P. schiedeanus during the Last Glacial period, with probable secondary contact leading to the new hybrid cluster. These results highlight the importance of Pleistocene climate cycles in the evolutionary history of Neotropical plants.